1. Field of the Invention
The present invention relates to a signal processing apparatus and signal processing program which correct limb darkening.
2. Description of the Related Art
The brightness of an image formed by a lens gradually decreases from the optical axis center of the lens to its edge. This phenomenon is called limb darkening. Light incident on the lens at an angle θ with respect to the optical axis is formed into an image at a position shifted from the lens center. The brightness of this image is proportional to cos4 θ.
As a method or apparatus for correcting this limb darkening, for example, the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-164194 is known.
In this method, a two-dimensional plane coordinate system having its origin at the optical axis center of an imaging plane is defined. The brightness of an image at the position of a point (x, y) in the two-dimensional plane coordinate system is corrected by using a correction expression using a distance R from the origin as a parameter. This reference also discloses a technique for performing limb darkening correction processing for each of the colors R, G, and B.
In this method, however, multiplication or square root extraction must be performed a plurality of number of times with respect to all points (x, y). It therefore takes much time to perform limb darkening correction, interfering with high-speed operation. In addition, this complicates the arrangement of an apparatus for realizing this limb darkening correction.
In addition, limb darkening correction processing for each of the colors R, G, and B requires much processing time because limb darkening correction processing is repeated for each color. If correction is to be made by using different limb darkening correction ratios for the respective colors, the arrangement of an apparatus for executing the processing becomes complicated.